In a patent to Buckley et al, U.S. Pat. No. 4,068,947, entitled "Optical Projection and Scanning Apparatus", there is described apparatus and methods for photographically exposing an image receiving surface to a light image of an object. This patent illustrates one use of the present invention in which a mask is used to project a light image through an optical system to a wafer.
In the aforementioned patent in FIGS. 12-16, there is described a wafer comprising a light sensitive object which is exposed to a succession of light images in closely controlled relative positions. The position of the wafer is more closely controlled than the mask so that the successive exposures will be in the correct relative positions.
The various mechanisms for positioning the mask and wafer with respect to each other are described in the aforementioned patent and may also be utilized in practicing the present invention. Details shown and described in this patent with respect to positioning the wafer are not illustrated with only the features particularly relating to the present invention being illustrated and described. Generally, the operation relating to the apparatus involving the present invention takes place after the final positions of the mask and wafer have been established and prior to the reproductions of the images on the wafer.